1. Field of the Invention
The present invention relates to image forming apparatus such as copying machines and laser beam printers, and to a recirculating document handler for use with the image forming apparatus or the like.
2. Description of the Related Art
In recent years, image forming apparatus have been proposed which are provided with a recirculating document handler on the glass platen of the apparatus for exposing documents to light and reading images thereof to eliminate the need for the user to place the document sheets one by one on the glass platen.
The recirculating document handler has a document containing portion for accommodating a stack of documents and delivering the documents by a feed roller one by one from the lowermost position, and transport means for transporting the delivered document onto the glass platen for image exposure or reading and thereafter returning the document onto the remaining stack of documents accommodated in the containing portion. With use of the handler thus constructed, a multiplicity of documents can be transported therethrough in circulation one sheet after another in the order in which they are stacked up, with the result that the documents can be fed to the glass platen in the stacked order and thereafter collected automatically.
The document handler further has a return document holder for holding the documents as stacked up in the containing portion when the document is delivered from the containing portion. When a sheet of document is returned while the holder is in the document holding position, the sheet of document is arrested by the holder on the documents set in the containing portion, whereby the returned document is distinguished from the set documents to be fed. The return document holder is integrally formed with a plurality of projections for holding the set documents at widthwise different portions thereof and for arresting the returned document. Nevertheless, the documents previously set in position are not always planar, or the document setting tray of the containing portion, feed mechanism or recirculating transport mechanism will produce undulations of documents or locally raise some documents, so that a clearance not infrequently occurs between the document and one of the plurality of projections which are integral with the single document holder.
Consequently, the projection in contact with the set document is likely to arrest the forward end of the returning document at a one-sided position, or the returning document will be arrested at only one portion. It is then likely that the returning document will skew under the raised projection owing to an uneven arresting action or unbalanced resistance involved in the return travel.
Such a skew will not always be fully corrected even if the returned document is set in the feed position again for the subsequent feeding. Furthermore, repeated transport of documents in circulation is likely to entail a greater disturbance. Consequently, the document will jam the handler, or copy images become oriented improperly.
Additionally, the return document holder is so disposed as to function at a position downstream, with respect of the feeding direction, from the feed roller for delivering the set documents from the containing portion one sheet after another at the lowermost position. Accordingly, the set documents are subjected to the transport action of the feed roller at a portion upstream from the portion thereof held by the holder. Thus, while being subjected to the transport action, the set documents are offered resistance against this action by being held by the holder at the downstream position. As a result, some of the set documents tend to deviate upward, forming a loop between the holding position and the position where the transport action is exerted thereon. This loop could lead to improper transport.
The document holder holds the stacked documents at all times, so that as documents are dispensed from the lowermost position, upper documents also inch forward, forming an upward loop between the document transport means in the downstream position and the document holder. This loop can also be a cause of faulty transport. The above problem becomes more serious as the number of set documents decreases or if the documents are thinner; the document becomes wrinkled and is therefore liable to cause a jam.
Further, with the image forming apparatus equipped with the recirculating document handler described, it is common practice to set the apparatus in a document moving scan mode wherein the document is scanned for image exposure or reading while the document is being transported in order to execute a high-speed process. In this mode documents are successively delivered from the containing portion at the greatest possible rate for continual image exposure or reading and are thereafter returned to the containing portion.
However, the return of the first document to the containing portion is likely to overlap the delivery of the final document from the containing portion owing to the conditions involved such as document size, number of set documents, feeding inverval or length of the document transport path. If the speed of return of the document to the containing portion is higher than the speed of delivery of the document therefrom at this time, the front end of the returning document impinges on the rear end of the document being delivered for feeding. It is then likely that the document to be fed or the return document will skew, or that the return document is positioned beneath the outgoing document and dragged along thereby for feeding. Consequently a document jam occurs or the last document is not handled properly for image exposure or reading through interference with by the first document.
The document handler described further has a document conveyor belt means in pressing contact with the upper surface of the glass platen for image exposure in the above-mentioned document moving scan mode. Depending upon where the image scan point is set on the glass platen or depending upon the size of documents to be handled, transport means such as transport rollers adjacently disposed to the conveyor belt means, on the upstream side of the conveyor belt means with respect to the direction of transport of the document and, along with the conveyor belt means extending along the platen at the same time, operates on the document moving past the image scan point.
It therefore follows that while moving past the scan point, the document is affected not only by the speed of transport by the conveyor belt means but also by the speed of transport by the transport means adapted to transport the document to the conveyor belt means and disposed upstream from the conveyor belt means with respect to the direction of document transport by the belt conveyor means. It is therefore often likely that the document image will not be scanned at a constant speed.
For example, suppose the speed of transport by pinch rollers upstream from the conveyor belt means is lower than that by the conveyor belt means, and the transport force of the conveyor belt means is smaller than that of the pinch rollers. When the document is in engagement with both the pinch rollers and the conveyor belt means, the document is transported at a low speed restricted by the transport speed of the pinch rollers, when released from the pinch rollers, the document is freed from the restraint by the transport speed of the pinch rollers. The document is then further transported at the high speed of the belt means. Thus, the document scan speed changes from low to high during scanning and fails to ensure a constant-speed scanning operation.
The conveyor belt means has a conveyor belt, a drive roller provided inside the belt for driving the belt, and a driven roller to be driven by the drive roller and biasing the conveyor belt in the direction of transport of the document. Accordingly, the conveyor belt is held tensioned at all times to transport documents with good stability. An adjacent transport path for accepting the document transported by the conveyor belt means is provided on the downstream side of the driven roller which is movable inside the conveyor belt. A transport guide is interposed between the driven roller and the adjacent transport path. It is desired that the distance between the transport guide and the portion of the conveyor belt biased by the driven roller (hereinafter referred to as the "movable tensioned portion") be held constant so that the document can be reliably transferred from the conveyor belt means to the adjacent transport path.
Nevertheless, the transport guide is fixedly provided, whereas the conveyor belt end immediately adjacent thereto is moved by the movement of the driven roller toward the document transport direction, altering the clearance between the movable tensioned portion of the conveyor belt and the transport guide. As a result, the document will not be guided properly when delivered from the transport path provided by the conveyor belt to the transport path afforded by the transport guide. Hence, there is a likelihood of a jam or of advance of the document in toward an improper direction.
The recirculating document handler described further has a container unit movable toward the document transport direction for receiving the document returned to the containing portion after the document has been fed to the document reading portion and transporting the document onto the remaining documents accommodated in the containing portion. The container unit, which is provided in the containing portion, has an upper portion greatly projecting beyond the upper surface of the containing portion, i.e. the top side of the document handler.
Since the document handler will be treated like the usual document cover, books or like articles will often be placed on the containing portion. If the container unit is moved in the document transport direction at this time, the upper portion of the container unit projecting above the containing portion will be under load from the article. Further, even if the book or like article is not placed on the document handler, the unit upper portion is likely to be underload from the operator during the movement of the unit since this portion is greatly projected beyond the top side of the document handler. When the container unit is thus loaded at its upper portion, there arises the problem of the load causing damage to the drive mechanism or the container unit.
The container unit is movable in the document feed direction to handle documents of different sizes to be returned to the containing portion. However, the container unit is adapted to accept documents of slightly different sizes without being moved, for example, to receive a document of legal size and thereafter receive a document of A4 size which is slightly different from the legal size. The container unit is so adapted by being provided with a document receiving opening which is tapered. The tapered opening enables the container unit to handle documents of slightly different sizes, whereas the receiving opening, which is too wide, permits the received document to warp, sometimes failing to receive documents properly with good stability.
The container unit has a discharge roller on its inside for discharging the received document to the containing portion and for transporting the document onto the stack of documents to be fed, and a guide wall disposed at the front portion, of the unit, with respect to the document feed direction, for pushing the rear end of the document during the transport with respect to the document feed direction. The document is likely to enter a space between the guide wall and the bottom plate of the containing portion. Furthermore, the friction between the document being transported and the bottom plate of the containing portion is likely to permit the document rear end to escape upward along the guide wall in sliding contact therewith. Such an escape of the document along the guide wall will occur also when the distance between the guide wall and the return document holder, or the distance between the guide wall and a feed document holder disposed downstream from the holder with respect to the document feed direction is made equal to the width of the document.